In U.S. Pat. No. 3,498,352 entitled Self-Locking Threaded Element in the name of R. J. Duffy dated Mar. 3, 1970 and assigned to the assignee of the present invention, there is disclosed a method and apparatus for making a self-locking threaded element by directing a stream of heat softenable resin particles against the threaded surface of a heated element. The procedure shown in the patent of supporting a series of threaded articles on a conveyor belt for heating and treatment with resin particles, presents the difficulty with a succession of internally threaded articles that resin is deposited on the end faces of the threaded elements.
Also, in U.S. Pat. No. 3,894,509 entitled Apparatus for Manufacture of Fasteners in the name of R. J. Duffy et al. issued July 15, 1975 and assigned to the assignee of the present invention, there is disclosed an apparatus and method for mass production of internally threaded self-locking elements including an arrangement for disposing a succession of heated internally threaded elements on a conveyor, with each element in association with an individual powder applying tube arranged to direct a stream of heat softenable resin particles upwardly through the lower opening of the element against the thread surface to form resin locking patches.
The method and apparatus of U.S. Pat. No. 3,894,509, while effective to form locking patches on internally fasteners at a very high production rate, requires a conveyor and powder applicator tube arrangement for each size of threaded fastener treated.